Field of the Invention
The present invention relates to an image pickup apparatus having a function of correcting defocusing that occurs according to an aperture difference and a method for controlling the same.
Description of the Related Art
Conventionally, in an image pickup apparatus such as an electronic still camera, as a method for moving a focus lens position to focus on a subject, an autofocus control (AF control) that automatically performs a focusing operation using an image signal from an image pickup device is used. If an aperture is changed after the focusing operation of the AF control, a defocused or blurred image may be shot.
In Japanese Laid-Open Patent Publication (kokai) No. 2005-352043, in order to correct defocusing caused by an aperture difference as described above, correction values for a plurality of apertures are written in the camera and correction is performed according to the aperture at a time of image shooting to improve focusing accuracy.
However, according to the related art disclosed in Japanese Laid-Open Patent Publication (kokai) No. 2005-352043 described above, when making correction values for correcting defocusing caused by the aperture difference, it is necessary to perform bracket shooting and store a lens position at which the subject is in best focus for each aperture (hereinafter referred to as “the best focus”). At this time, to improve the accuracy of calculation of the best focus, the processing time becomes longer for the following points (1) to (3).
(1) It is necessary to increase sampling of bracket shooting.
(2) To calculate best focus (position where a high-frequency component peaks), it is necessary to perform a multiple order approximation.
(3) To reduce optical defocusing (defocusing caused by lens aberration), it is necessary to read a non-added image similar to a still image and to perform a process for evaluating best focus in a high-frequency band.
Therefore, creating a correction value for each individual during mass production will lead to an increase in adjustment time with decreased productivity.
Furthermore, in an image pickup apparatus or the like with an attached lens, even if an adjustment is made based on optical characteristics of a sensor before mounted in a housing, adjusted values may shift during housing assembly.